Personal digital assistants (also called PDAs) are handheld devices that were originally designed as personal organizers, but became much more versatile over the years. A basic handheld PDA usually includes date book, address book, task list, memo pad, clock, and calculator software. Newer PDAs also have both color screens and audio capabilities, enabling them to be used as mobile phones, web browsers or media players. Many PDAs can access the Internet, intranets or extranets via Wi-Fi, or Wireless Wide-Area Networks (WWANs).

Many original handheld PDAs featured touch screens for user interaction, having only a few buttons usually reserved for shortcuts to often used programs. Touch screen handheld PDAs, including Windows Pocket PC devices, usually have a detachable stylus that can be used on the touch screen. Interaction is then done by tapping the screen to activate buttons or menu choices, and dragging the stylus to for example highlight text.